Abstract 3182: Paracrine Contribution versus Direct Regeneration in Cardiosphere-Derived Cell Therapy for Acute Myocardial Infarction
Human cardiosphere-derived cells (CDCs) have been previously shown to improve LV function in a SCID mouse model of cell therapy for acute myocardial infarction (AMI). CDCs have been shown to contribute to regeneration through direct differentiation, but the potential role and relative importance of paracrine mechanisms remain unclear. This study addresses the paracrine effect by quantifying total measurable benefits and quantifying those attributable to direct differentiation. CDCs were grown from endomyocardial biopsies from 8 patients. CDCs, or normal human dermal fibroblasts (NHDFs) as control, were injected intramyocardially into the border zone of AMI in SCID beige mice (105 cells). In vivo tracking of luciferase-labeled CDCs showed a decline in light at 1 week to 31±9% of the day 1 signal (n=6). After 1 week the peri-infarct area of CDC-injected hearts displayed higher protein levels of Akt and decreased Caspase3 compared to NHDF-injected hearts. This correlated with a reduced rate of TUNEL positive cells (17.1±7.6 vs 44.4±8.2 TUNEL+/mm2; n=35 fields; P=0.03) and increased capillary density (0.31±0.02 vs 0.16±0.02 capillaries/nuclei; n=57 fields; P<0.001) in peri-infarct tissue sections. In the areas where CDCs had engrafted, 9.6±2.7% of the capillary counts were found to be of human origin, as demonstrated by double staining for isolectin B4 and human nuclear antigen (HNA; n=226 human nuclei), which accounted for only a small fraction of the overall doubling in capillary density. Furthermore, the infarct area of CDC-injected mice contained a higher percentage of viable myocardium (49.7±6.0 vs 40.1±6.8%; n=20; P=0.004), as assessed by Masson’s trichrome staining; within those viable areas, 11.8±4.5% of the myosin heavy chain (MHC)-expressing cells were also HNA positive (n=412 human nuclei). No capillaries or MHC-positive cells of human origin were detected in the NHDF-treated group. Altogether these results suggest that the residual engraftment of CDCs and their direct differentiation cannot alone account for the overall beneficial effects observed in cardiac function and tissue viability, and demonstrate for the first time that much of the positive outcome is in fact due to indirect pro-survival and pro-angiogenic paracrine mechanisms.